Abstract/ Project summary Malaria caused by Plasmodium spp parasites is a leading cause of morbidity and mortality globally. The emergence of resistance to frontline antimalarial drugs threatens to wipe out progress made in disease control and set back efforts toward eradication. New drug targets are urgently needed to circumvent current resistance mechanisms. The unique biology of Plasmodium spp and related human pathogens, compared to their mammalian hosts, can be leveraged to discover pathogen-specific drug targets that minimize host toxicity. A prime example of the pathogen's distinct biology is the non-photosynthetic plastid organelle, or apicoplast. Critical proteins that govern the biogenesis ? growth, division, and inheritance ? of the apicoplast during parasite replication remain mysterious, though compounds that block apicoplast biogenesis, such as clindamycin, are used clinically to prevent malaria and treat malaria, babesiosis, and toxoplasmosis. Because apicoplast biogenesis is required in every proliferative stage and conserved among parasites, it presents untapped opportunities to discover pathogen-specific drug targets effective across life stages and against multiple pathogens. Our long-term goal is to discover the molecular mechanisms of apicoplast biogenesis and exploit the machinery involved as antimalarial targets. The objective of this project is to identify and functionally characterize genes required for apicoplast biogenesis in blood-stage P. falciparum, since many essential, but as yet unidentified, genes are required for this complex process. My laboratory has laid the foundation to achieve this objective by successfully designing innovative approaches to discover new molecular players. This proposal will identify previously unknown genes required for apicoplast biogenesis using a new forward genetic screen and begin characterizing the biochemical and cellular functions of newly-validated genes. By identifying and functionally characterizing apicoplast biogenesis proteins, we will understand how this process can be disrupted to block pathogenesis in multiple stages of multiple eukaryotic pathogens.